Pyrotechnic lacquer

ABSTRACT

LACQUERS COMPRISING A DISPERSION OF A PYROTECHNIC COMPOSITION IN A COLLODION, WHICH ARE USEFUL IN FORMING IGNITION COATINGS ON BLOCKS OF PROPELLANT AND GAS GENERATORS, THE PYROTECHNIC COMPOSITIONS MAY BE ALUMINO-THERMAL POWDERS, THERMITES, BLACK POWDERS OR ZIRCONIUM/BARIUM CHROMATE/AMMONIUM PERCHLORATE/AMMONIUM BICHROMATE, AND THE COLLODION MAY BE A NITROCELLULOSE OR NITROGLYCERINE POWDERS (OR MIXTURES OF THE TWO), OR A PLASTICS MATERIAL, IN SOLUTION IN SOLVENT.

Feb- 26. 1974 Y. H. BERTRAND ETAL PYROTBCHNIC LACQUER Filed July 14,1972 3 Sheets-Sheet l Feb. 26, 1974 Y. BERTRAND ETAL 3,794,535

PYROTECHNIC LACQUER 5 Sheets-Sheet 2 Filed July 14, 1972 fur-4 Feb. 26,1974 Y H BERTRAND ETAL 3,794,535

PYROTECHN I C LACQUER Filed July 14, 1972 3 Sheets-Sheet a 3 01.6 9 liz1,'5 1,18 2i. I4 7 3.10Y

United States Patent Office Patented Feb. 26, 1974 U.S. Cl. 149-3 7Claims ABSTRACT F THE DISCLOSURE Lacquers comprising a dispersion of apyrotechnic composition in a collodion, which are useful in formingignition coatings on blocks of propellant and gas generators. Thepyrotechnic compositions may be alumino-thermal powders, therrntes,black powders or zirconium/barium chromate/ammonium perchlorate/ammoniumbichromate, and the collodion may be a nitrocellulose or nitroglycerinepowders (or mixtures of the two), or a plastics material, in solution insolvent.

The present invention relates to a pyrotechnic lacquer used especiallyfor producing ignition compositions for blocks of solid propellant andcharges for gas generators.

According to the invention, there is provided a lacquer which comprisesa dispersion of: (a) a pyrotechnic composition in a tinely divided form,chosen from the group comprising aluminothermal powders (a mixture ofpotassium perchlorate and aluminium powder), `flo-called thermitepowders (a mixture of potassium perchlorate, iron oxide and magnesium),black powder and powders based on zirconium, barium chromate, ammoniumperchlorate or ammonium bichromate, in (b) a collodion containing eithera powder based on nitrocellulose, on plasticized nitricellulose or on amixture of nitrocellulose and nitroglycerine, dissolved in a volatilesolvent for the said powder, especially a ketone solvent such as acetoneor methyl ethyl ketone, or a plastics material dissolved in an organicsolvent, especially polyethylene dissolved in trichloroethylene,polyvinyl chloride dissolved in methyl ethyl ketone or a cellulosicpolymer dissolved in ethyl acetate.

The proportions in which the pyrotechnic composition and the collodionare used are from 5 to 99.5%, preferably from 40 to 60%, by weight forthe former and from 95 to 0.5% and preferably 60 to 40%, by weight ofthe latter. Furthermore, the collodion preferably contains 75% by weightof powder or of plastics material and 25% of solvent.

Additionally, the pyrotechnic composition should preferably have aparticle size of less than 500 microns.

The pyrotechnic lacquer of the invention is especially useful as anignition composition for blocks of solid propellant. For this purpose,that face of the block to be ignited is coated with a layer of thepyrotechnic lacquer and the solvent is evaporated. The ignitioncomposition thus obtained can advantageously replace the conventionaltriggering box containing black powder, which is usually fixed by glueto a face of the propellant block and which can become detached andthereby cause spoilage of the guide system during ignition.

The pyrotechnic lacquer according to the invention can also be used toproduce pyrotechnic charges for gas generators of the type described inour French patent applications Nos. /44,837 and 70/44,838. For thispurpose, the outer wall of the vaporizable liquid chamber of the gasgenerator is coated, partially or completely, with the pyrotechniclacquer of the invention and the solvent is evaporated from the layer oflacquer.

The pyrotechnic lacquers of the invention have numerous advantages:

they do not require baking and polymerization operations; they arestable on storage in a leakproof container; and their speed ofcombustion can easily be varied by varying the charge content or bychanging the nature of the collodion or the nature of the pyrotechniccomposition.

In order that the invention may be more fully understood, the followingexamples are given by way of illustration only. In addition, referenceis made to the accompanyng drawings, in which:

FIG. l is a cross-section in side elevation of a block of propellantprovided with a layer of a lacquer of the invention;

PIG. 2 is a front elevation of the same block;

FIGS. 3 and 4 are graphs illustrating the results of experiments carriedout in vacuo on the pyrotechnic lacquer and on the propellant: and

FIGS. 5 and 6 are graphs illustrating the ignition phase of tirings ofthe blocks of propellant of Examples 2 and 3, respectively.

EXAMPLE 1 Preparation of the pyrotechnic composition 45 parts by weightof zirconium, 34 parts of barium chromate, 14 parts of ammoniumperchlorate and 7 parts of ammonium bichromate were mixed together bymeans of a Moritz mixer running at low speed, for one hour.

Preparation of the collodion parts by weight of GB Tu powder (a powderbased on nitrocellulose and on nitroglycerine, in the ratio of 58:42,containing 1.1% of centralite as a stabilizer) were dissolved in 25parts of acetone.

Preparation of the pyrotechnic lacquer 60 parts by weight of thepyrotechnic composition were mixed with 40 parts of collodion. Mixingwas carried out in a climatically controlled area at 2l-29 C. and 30-40% relative humidity.

The pyrotechnical lacquer thus obtained was used to produce, by coating,an ignition composition on a block of Epictte propellant plasticizednitrocellulose and njtroglycerine) for frontal combustion, of which acrosssection in side elevation is shown in FIG. l of the accompanyingdrawing, and a front elevation in FIG. 2.

This cylindrical block l, diameter 78 mm., was perforated by an axialcylindrical channel 2, 1.5 mm. in diameter, and was covered with a layerof inhibitor 3 on its side wall, in the said channel and on its frontface.

The rear face 1a of this block was coated with a layer 4 of thepyrotechnic lacquer prepared above, 5 g. of this lacquer being uniformlyspread over a ring of external diameter 60 mm. and internal diameter l0mm.

The layer of lacquer was thereafter dried in a climatically controlledarea at 21-29 C. and at 30-40% relative humidity for several hours inorder to produce, on this block of propellant, a layer of ignitioncomposition of about 1 mm. thickness.

The compatability of the pyrotechnic lacquer with the propellant wasdemonstrated by the following tests:

Vacuum test This test was carried out at temperature of 90 C., 100 C.and 110 C.

The test sample, for a test at a given temperature, was l g.

Vacuum test-test on the pyrotechnic lacquer In view of the highsensitivity of the composition to mechanical pyrotechnic factors, thistest was carried out on a dry mixture of 2 parts of the said pyrotechniccomposition and of 3 parts of finely ground collodion slab.

The results shown on the graph of FIG. 3 give, the pressure loss in mm.(as the ordinate) as a function of the time in days (as the abscissa).

Vacuum test"-on chips of propellent The results are shown on the graphof FIG. 4.

superposition of the graphs of FIGS. 3 and 4 shows an identicalbehaviour of the propellant and of the pyrotechniccomposition/collodion" mixture in the experiments of the vacuum test.

Furthermore, the resistance to ageing of the ignition compositionobtained from the pyrotechnic lacquer was demonstrated by the so-calledtest cube test.

The study was based on ageing for two to six months at 60 C. The testswere carried out on four cubes of 25 mm. side length, of which one facewas entirely coated with pyrotechnic lacquer to a thickness equivalentto that produced on the block of propellant.

A test cycle comprised:

(a) 18 hours temperatuure exposure in an oven thermostated to :L- l.50C. and

(b) Removal from the oven for 6 hours, during which a visual andradiographic check of the propellant-ignition composition interface wasmade on each cube.

The results obtained after 22 cycles at 60 C. were that, at 60 C., nodetachment of the ignition composition, and no cracking in thepropellant, was observed.

EXAMPLE 2 A pyrotechnic lacquer was prepared by mixing 40 parts byweight of a thermite powder of the following composition:

Percent Fe203 34 Mg 36 KC104 30 with 60 parts of collodion of the typedescribed in Example l.

The face of a Butalpite block of propellant (polybutadiene-potassiumperchlorate) which was to be ignited, of diameter 94 mm., was coatedwith 5 g. of this lacquer.

The graph in FIG. 5 shows the pressure in bars (as the ordinate) as afunction of the period of combustion in seconds (as the abscissa),illustrating the ignition phase of a tiring using the block ofpropellant which was ignited by means of the pyrotechnic lacquer of thisexample, applied by coating.

EXAMPLE 3 A pyrotechnic lacquer was prepared by mixing 40 parts byweight of blackpower with 60 parts of collodion of the type described inExample 1.

The face of a homogenous block of powder(nitrocellulose-nitroglycerine), 33 mm. in diameter, was coated with 5g. of this lacquer.

The graph in FIG. 6 shows the pressure in bars (as the ordinate) as afunction of the period of combustion in seconds (as the abscissa),illustrating the ignition phase of a firing using the block ofpropellant which was ignited by means of the pyrotechnic lacquer of thisexample, applied.

EXAMPLE 4 A pyrotechnic lacquer was prepared by mixing 2 parts by weightof a thermite powder having the following composition:

Percent Fe203 34 Mg 36 KClO4 30 with 3 parts by weight of a collodion ofthe type described in Example I.

This lacquer was directly coated onto the outer wall of the vaporizableliquid chamber of the gas generator described in Belgian Pats. 775,997and 775,422, both granted Dec. l5, 1971, to which correspond U.S.applications, Ser. No. 206,662 and Ser. No. 205,046, and was dried in aclimatically controlled area at 2129 C. and at 30-40% relative humidityfor several hours so as to yield a 2.25 mm. layer of a gas generatorcomposition, as a replace ment of the charge of propellant in hollowstrands, with which the said gas generator was equipped.

We claim:

1. A lacquer which comprises a dispersion of: (a) a pyrotechniccomposition in finely divided form, selected from the group consistingof powders consisting of (l) ferrie oxide, magnesium and potassiumperchlorate, (2) of black powder and (3) of powders consisting ofzirconium, barium chromate, ammonium perchlorate and ammoniumbichromate. in (b) a collodion which consists of a powder based onnitrocellulose and nitroglycerine cerine dissolved in a ketonic solvent,the dispersion containing from 40 to 60% by weight of the pyrotechniccomposition, and from 60-40% by weight of said collodion.

2. A lacquer according to claim 1 which comprises a dispersion of 3parts by weight of a pyrotechnic composition consisting of zirconium,barium chromate, ammonium perchlorate and ammoium bichromate in therespective proportion 45:34: 14:7, in 2 parts by weight of a collodionconsisting of 75% of a power based on nitrocellulose and nitroglycerinein the respective proportions of 58 to 42 and containing 1.1% ofcentralite and 25% of acetone.

3. A lacquer according to claim 1, which comprises a dispersion of 2parts by weight of a pyrotechnic composition consisting of FegOs, Mg andKCIO4 in the respective proportions 34:36:30 in 3 parts by weight of acollodion consisting of 75% of a powdei based on nitrocellulose andnitroglyoerine in the respective proportions of 58 to 42 and containing1.1% of centralite and 25% of acetone.

4. A lacquer according to claim 1, which comprises a dispersion of 2parts by weight of a pyrotechnic composition consisting of black powderin 3 parts by weight of a collodion consisting of 75% of powder based onnitrocellulose and nitroglycerine in the respective proportions of 58 to42 and containing 1.1% of centralite and 25% of acetone.

5. A solid propellant grain having an ignition face coated with a layerof a lacquer which comprises a dispersion of: (a) a pyrotechniccomposition, in finely divided form, selected from the group consistingof (1) powders consisting of ferrie oxide, magnesium and potassiumperchlorate, (2) black powder and (3) powders consisting of zirconium,barium chromate, ammonium perchlorate and ammonium bichromate in (b) acollodion which consists of a powder based on mixtures of nitrocelluloseand nitroglycerine, said powder being dissolved in a ketonic solvent,the dispersion containing from 40 to 60% by weight of the pyrotechniccomposition and from 6() to 40% by weight of said collodion.

6. A charge for a gas generator comprising a vaporizable liquid chamberhaving an outer wall, said charge consisting of a layer of lacquercoating said outer wall, said lacquer comprising a dispersion of: (a) apyrotechnic composition, in nely divided form, selected from the groupconsisting of powders consisting of ferrie oxide, magnesium andpotassium perchlorate, black powder and powders based on zirconium,barium chromate, ammonium perchlorate and ammonium bichromate in (b) acollodion which consists of a powder based on mixtures of nitrocelluloseand nitroglycerine, said powder being dissolved in a ketonic solvent,the dispersion containing from 40 to 60% by weight of the pyrotechniccomposition and from 60 to 40% by weight of collodion.

7. A lacquer according to claim 1 wherein the ketonic References CitedUNITED STATES PATENTS ONeill et al. 149--96 X Ryker et al 149-96 XONeill 149-96 X Vandersmith et al. 149-10 X Coffee 149-96 X Herzog et al149-96 X Hamilton 149-8 X STEPHEN I. LECHERT, JR., Primary Examiner U.S.CI. X.R.

solvent is selected from acetone and methyl ethyl ketone. 15 149-8, 12,38, 40, 42, 44, 65, 73, 76, 85

